I'd really be weighing the pros and cons here. You're living in a horrible living situation that's very unhealthy (you are living in the room with the fibreglass right? And have the roommate who doesn't take care of his cats? If those ones weren't you... then I am sooooooooooo sorry but my memory doesn't always connect threads!) and it would be in your best interests to get out of it.

Who all is your friend connected to that she will gossip with, if she gossips? What is the most likely result if she was to talk about it with others? (As in, not the most feared result. What do you actually think is the most likely result of the people you know learning about your diagnosis)?

What are you like when you are manic and can't hide things? What sorts of things do you do? Could they be passable as something else?

Personally, I'd probably take the chance to get into a healthier environment. And then I'd risk explaining it only after I'd lived with her for a while - after all, I might hate living there anyway. I wouldn't self-disclose until I thought I was at a point that I needed to - I'm sure your boyfriend would help with that.